Pet owners desiring to keep their pets within a defined boundary are considering alternatives to traditional fences. Currently, there are several electronic fences or boundaries that serve as alternatives. One such alternative is a buried wire fence, and another is a distributed transponder fence as described in U.S. Pat. No. 5,241,923. There are several electronic fences or boundary control systems that require no buried wires or transponders. The fenceless animal control system described in U.S. Pat. No 5,868,100 determines animal location using GPS satellites and a reference ground station for improved accuracy.